In most industrial sites, such as refineries, steelworks, mining facilities, bauxite treatment and the like, there are heat exchangers used to cool the equipment which operates according to cycles of varied temperatures, in which air or a heat-transfer fluid such as water circulates. The heat is evacuated by passing a fluid through pipes, generally made of steel or of an iron-based alloy.
Periodically, in order to prevent the accumulation of scale, soiling, sludge, algae, salts and various deposits in these pipes, an acid treatment composition is circulated in order to especially clean and, in particular, to dissolve the scale, followed by a second, alkaline solution in order to neutralize the residual acidity, before repeating a conventional exchanger cooling cycle.
Similarly, certain treatments for chemical pickling of metal surfaces are carried out by immersion in acid solutions.
In order to avoid corrosion of the steel by the acid solution, corrosion inhibitors are generally added to the acid treatment composition. Among them, thiourea derivatives, such as dialkylthioureas, are often used for their good stability at very low pH.
Other agents, for instance antifoams, in particular antifoam silicones, recommended for their good resistance to strongly acidic media, are also present most of the time in the treatment composition in order to avoid uncontrollable foam formations which would make the cleaning operations longer and more difficult.
However, the simultaneous presence of an antifoam and of an anti-corrosion agent of the thiourea type can, in certain cases, accelerate the corrosion of the metal surfaces, said corrosion being perceived through weight loss or the appearance of pitting on the surfaces, whereas this corrosion and therefore their weight loss is much less if the treatment composition contains only the thiourea derivative. However, in this case, the problem of the appearance of bothersome foams during the use of the treatment composition of course persists and one of the objectives of the present invention is precisely to propose a technical solution to the problem stated above.